Method of conditioning cylinders and the like



Patented Sept. 2, 1941 METHOD OF CONDITIONING CYLINDERS AND THE LIKECharles W. Latham, Maspeth, N. Y., assignor to Smart Platen Process 00.,

Inc., Brooklyn,

No Drawing. Application February 23, 1940, Serial No. 320,423

Claims.

My invention relates to a method of truing cylinders, platens, and thelike, and the principles and steps thereof are disclosed herein using anoffset printing press by way of example.

In offset lithography the press has at least three cylinders, one towhich the printing plate is fastened or strapped, a second or middle onewhich carries a transfer blanket usually of rubber, and a third cylindercarrying the paper on which the final impression is made. The plate onthe plate cylinder is inked by rollers, the image on the plate beingtransferred to the blanket, and from the blanket to the paper.

It is highly important that during operation the surface of these threecylinders travel at exactly the same number of feet per second, whichfor purposes of this discussion can be assumed to be the same asrotating the cylinders at exactly the same number of revolutions perminute. If this is not done, there will be smearing and streaking, and ageneral lack of clarity and definition in the final print. In computingthis peripheral speed there must be added to the actual diameters of theplate and blanket cylinders the thickness of the plate and the blanket.respectively, and also sufficient packing behind the blanket to give thenecessary printing pressure to obtain adequate transfer. This packingusually consists of sheets of paper and the additional squeeze forprinting is best obtained with .004" of packing in addition to whateveris necessary to have the three cylinders uniform in diameter.

Any pressure between the cylinders in excess of that indicated willproduce undesirable printing results. However, the cylinders warp andbend under the stresses and strains of continuous work, and are oftendeformed by bits of cloth, wood and other foreign materials enteringbetween the cylinders. Heretofore, the pressman has endeavored tocompensate for such conditions by inserting patches of paper behind theblanket to fillup the hollows and low places in the cylinders, or hasresorted to other make- 45 shift ways in his endeavor to maintain aneven pressure over the entire surface of the cylinders. It is apparentthat such methods cannot be accurate as a practical matter, and one ortwo thdusandths additional packing on one or more of the high spots ofthe cylinders will give the excess pressure that causes trouble.

"- ."The known method of reconditioning and truing of cylinders toobtain proper printing pressure is by re-surfacing and regrinding thecylinders which involved dismantling the press,

removing the cylinders, transporting them toa properly equipped plant,building up the surface of the cylinder to an excess thickness, thenprecision grinding the face of the cylinder, after which the cylindersare reinstalled in the press. Such procedure is expensive and requiresthe shut-down of the press for a considerable number of days.

It is one object of the present invention to provide a method ofpermanently building up the low spots of a cylinder or the like withoutremoving the cylinder from its normal mountmgs. i

It is another object of my invention to provide a simple and efficientmethod of quickly and accurately truing the surface of a cylinder or thelike.

It is a further object of my invention to provide a method of buildingup the working face of a cylinder or the like with base, intermediateand outer layers, each of different character.

It is a still further object of my invention to provide materials ofparticular characteristics for use in my process for truihg cylinderfaces.

Another problem in connection with lithographic and printing pressesfrequently arises fromthe corrosive effects of certaininks upon metalcylinders. My improved process contemplates the use of coating materialsto protect the surface of a cylinder or the like from the corrosiveeffects of inks and other materials as well as the air.

In practicing my invention, the cylinder being repaired is firstproperly cleaned and conditioned after whicha base lacquer coating isapplied followed by a coating of pigmented lacquer. Any nicks or deepimpressions are filled up. The cylinder is now ready for building up thelarger hollows thereof to the level of the high spot or spots of thecylinder. A masking cream is applied to the cylinder in such manner thatthe masking cream covers only the high spots of the cylinder, afterwhich the operator sprays a layer of pigmented lacquer over the entiresurface of the cylinden'including the parts covered with the maskingcream. The parts of the cylinder to which masking cream was applied arewashed off to remove the masking cream and the superimposed layer ofpigmented lacquer. Next, masking cream is again applied to the surfaceof the cylinder in such manner as to cover all the high spots thereof,and this is followed by another layer of pigmented lacquer.

These steps are repeated successively until all parts of the cylinderare brought up even. with the highest areas thereof, after which a finalsurface lacquer coating is applied. The characteristics of the materialsused, as well as'the details of operation in carrying out the steps ofmy process, as well as the drying times, etc., are all fully explainedhereinafter.

' In the course of usage of an offset press, the.

most seriously affected cylinders are the blanket and impressioncylinders. At times the plate cylinder may be affected also, but this isnot so usual partly because the surface is protected by the plate. Thecarrying out of the invention will be described in connection withconditioning the blanket and impression cylinders and on the assumptionthat the plate cylinder is in perfect condition or substantially so.

It will be understood, however, that the same principles are applicableto conditioning the cylinders of lithographing and printing presses, aswell as cylinders and platens used for many other purposes outside ofthe printing field as, for example, in the making of paper and themaking of paper doilies, napkins, and the like, in which parts are cutout to give lace effects, and advertising mounting cut-outs.

The first step of this process is to clean and condition the cylinder tobe built up. In offset lithographing presses, the working face of thecylinder becomes covered with oil and grease, some of which haspenetrated into 'the pores of the metal, and must be removed, along withother foreign matter, preferably down to the base metal of the cylinder.of course, dry ink, rust spots, and otheradhering matter may be quicklyremoved from the cylinder by scraping and sandpapering, after which thecylinder should be thoroughly washed with a solvent and softener for theink. Such softeners are usually of agesoline nature, such as xylol, andof light viscosity. This washing of the cylinder must be sufficient toremove all surface grease. after which the cylinder is coated with asubstance of a nature to saponify and emulsify ink and the ingredientsthereof, and to penetrate into the pores of the metal to clean the sameas well as the surface of the cylinder.

One such substance which I have found to be satisfactory consists of a.caustic alkali, such as lye, water, and a small quantity of starch, suchas ordinary laundry starch, mixed to form a paste which can be appliedto the cylinder and allowed to remain thereon. This coating mustcompletely cover the cylinder and preferably should be a thick coatingwhich will be allowed to remain on the cylinder at least one halfhour.

After this elapsed time, the caustic coating must be thoroughly washedoff, which is preferably done with water and sponge.

While the cylinder is wet from washing off the caustic, the cylindershould be washed next with a solution which will neutralize the causticalkali, and at the same time remove any iron oxide that may remain onthe cylinder. I have found ten percent solution of acetic acid to besatisfactory for these purposes, under normal conditions. Other acidsmay be used in a solution having a pH range of from 2 to 3. i

The whole cylinder should be washed off with this acid solution at leastthree times which should be suiiicient to remove any traces of thecaustic alkali and to start removal of the iron oxide. Whether thisremoval is by reduction or dissolution of the iron oxide, or both, isimmaterial, the desired eifect being to attack the face ,of the cylinderso as to roughen the same slightly in preparation for receiving thefollowing coatings. It is desirable that several additional applicationsoi the acid solution should be made, each without waiting for thepreceding application todry, so as to get down to the base metal of thecylinder, but apparently it is not necessary that every trace of theiron oxide should be removed.

After the last washing with the acid solution, and without drying thecylinder, the cylinder is washed with clear water until it is entirelyclean. This water will cause the formation of a very slight amount ofiron oxide, which is not harmful, the water being promptly worked offthe cylinder by means of a cloth saturated in the solvent of gasolinenature first referred to above. This working over the surface of thecylinder should continue until the surface is substantially uniform incolor, which will be a very light yellow.

It will be understood that with cylinders, etc., not used in a printingpress, that there may not be the necessity-for using the caustic coatingreferred to above, and that substitutions in the above materials may benecessary or advisable in order to meet conditions in the differentfields.

The important thing is that all foreign matter should be removed fromthe cylinder surface to be treated, as well as the surface pores, andthat the surface should be slightly roughened. If the acid treatmentdoes not produce sufficient roughening of the surface, then mechanicalmethods of roughening may be used, such as sand blasting, grinding, etc.

The next step in truing the cylinder is to apply the first of a seriesof coatings to build up the same, immediately preceding which operationthe cylinder should be washed with any usual lacquer thinner or alcoholto insure that the surface is free from moisture, grease and dust.

The initial or base coating applied to the cleaned face of the cylinderis preferably a nitrocellulose base .clear lacquer primer, desirablyhaving a plasticiser therein, so that the finished coating is smooth andcontinuous. This lacquer has the further characteristics of being ableto penetrate into the pores of the base metal of the cylinder andadheres firmly to the same; relatively slow drying, and such as to leavea tough, clear, somewhat resilient coating. Any usual type of spray gunis used to apply this coating, preferably as a wet spray, so as to leavea coating of substantial thickness, viz., of the order of .005". Ofcourse, the coating also must be of a nature to firmly bond with thefollowing lacquer coating.

The base coating should be allowed to dry for at least a half an hour,and preferably for one hour. It is also desirable that the cylinderberotated during this drying so as to insure an evenly distributedcoating. In applying the base coating, care should be taken tocompletely cover the edges as well as the face of the cylinder so as toleave no opening for moisture to creep in, thereby starting undesiredrust formation under the coatings. This same technique is used inconnection with the second coating which is to be applied as soon as theinitial coating is dry.

The second coating and all of the subsequent build-up coatings are alsosprayed on. This second coating is a pigmented nitro-cellulose baselacquer, which also preferably contains a plasticiser, and is desirablyquick drying. The pigmentation is preferably bronze, or other metal, inthe form of a powder having a particle size such as will pass through a200 to 400 mesh screen. We have found bronze having a particle sizeequivalent to 325 mesh to be very satisfactory in providing a coating ofapproximately .005" in thickness. A lacquer thinner is used to provide alacquer of a consistency of thin syrup.

The cylinder is now ready to have the intermediate coatings applied tobuild up the low spots thereof to the level of the high spots of thecylinder, which is accomplished in the following manner. According tothis process it is desirable to mask the high spots of the cylinder sothat subsequent lacquer coatings will not adhere thereto. In a printingpress the masking material can be applied in the form of a cream bymeans of the normal inking rollers. My masking cream comprisesapproximately equal parts of a printing ink, a blank fix, such as bariumsulphate pigment and a stock consisting of a soap which is high inalkali content, an oil such as lard oil, the soap and oil being of acharacter to saponify the ink, and enough water to form a soft paste.The same are mixed to a consistency such that a substantial film will betransferred to the cylinder.

In an offset press, and assuming that it is the normal blanket cylinderthat is first being conditioned, a blanket is attached to the normalplate cylinder, in place of a plate. 'The inking mechanism is operatedin the usual manner to apply a thick, even coat of masking cream to theentire blanket. i

When these preparations are made, and even before the masking cream isapplied to the blanket, the normal adjustments of the spacing betweenthe plate and blanket cylinders is made until only a light contactpressure exists between the blanket on the plate cylinder and the highspots'of the face of the normal blanket cylinder. After the cylindersare brought to contact position the adjustments are locked in place, andthe coated blanket and cylinder being conditioned are rotated. The highspots on the face of the blanket cylinder will receive a layer of themasking cream, which will cover the same. Those parts of the cylinderwhich have no masking cream thereon are the low spots which need to bebuilt up.

Of course, it has been assumed that dents and nicks in the base metal ofthe cylinder have been filled, which I prefer to do after theapplication of the base coatings referred to above and before firstapplying masking cream to the cylinder.

Having applied a coating of masking cream to the high spots of thecylinder, the operator then applies the first of the intermediatecoatings, which consists in spraying over the entire face of thecylinder, including the parts which have received the masking cream, acoating of the pigmented lacquer referred to above.

By the time the operator has completed applying this coat of lacquer tothe cylinder, that which was first applied is dry, but if not thecylinder may be allowed to dry for a few minutes, preferably whilerotating. The operator then washes off all the high spots of thecylinder which contain the masking cream and an overlying coating oflacquer, by using a, cloth saturated in a solvent and softener for theink, such as xylol referred to above. These spots are easily identifiedbecause there is a certain amount of coagulation takes place between thenewly applied coating of lacquer and the masking cream, which makes thatportion of the cylinder surface different in appearance from theremainder of the face of the cylinder. This method of removing theapplied coating of lacquer and the masking cream prevents the formationof any ridges around the high spots of the cylinder so that at the endof the building up process the cylinder will have a smooth andcontinuous surface.

This operation completed, a fresh coating of masking cream is applied,using the .same press adjustments that were used to apply the initialcoating of masking cream. This second coating of masking cream isapplied in the same way, and this time in addition to the high spotsinitially covered, it is probable that there will be additional highspots which also will receive the masking cream coating.

The operator then sprays upon the entire face of the cylinder andincluding the portions covered with masking cream, another coating ofthe pigmented lacquer, after which the high spots are again washed off.These steps of applying the masking cream, applying a coating ofpigmented lacquerto build up the low spots, washing off the maskingcream to remove the unwanted lacquer coating, and then remasking thecylinder, are repeated in that order until finally the whole surface ofthe blanket cylinder receives an even coating of masking cream.

Of course, there would be no objection 'to an experienced operatorfilling up a particularly hollow spot with several coatings of thebuilding up lacquer before applying a coating of masking cream, but atall times great care must be taken not to overlap the high spots with abuild-up coating unless there is masking cream over-the high spots.Also, it is desirable that there be only one coating of build-up lacquerapplied over an area having masking cream thereon so as to insure thecomplete removal of both masking cream and unwanted lacquer, which wouldotherwise produce ridges in the surface.

Having reached the point where the surface of the cylinder is completelytrued up, as shown by the complete layer of masking cream thereover, itis desirable that one additional coating of pigmented lacquer be appliedover the entire builtup surface of the cylinder as soon as the maskingcream is washed off.

Thus, the surface of the cylinder will be uniform in color, which mightnot be the case where I there have been alternate masking cream andpigmented lacquer coatings on different spots of the cylinder.

In any event my process contemplates applying one or more final finishcoatings of a clear lacquer, chosen to provide a hard and glossysurface, over the face of the cylinder. This lacquer is also denser thanthe two preceding lacquers referred to.

Having thus conditioned the blanket cylinder, the impression cylinder istrued up in exactly the same manner with the exception that the blanketis applied to its cylinder, a plate is put in place on the platecylinder, and in this case the masking cream is transferred from theplate to the blanket and thence to the impression cylinder.

It may be noted that in place of the masking cream described above,other masking creams can be used, as well as any of the types of waxcompounds normally used in lithographing inks to prevent smearing whenprinted sheets are piled on each other. Also, instead of metal powdersas referred to above, other pigments may be used in the lacquercoatings.

Furthermore, while the application of masking cream from the normalinking rollers has been referred to here, it will be understood that anyother arrangement could be used which will insure a uniform coating ofmasking cream from a level surface being brought into contact with thehigh spots of the cylinder being conditioned.

From the foregoing description, it will be seen that I have provided aprocess for building up cylinders, platens and the like to have asmooth, even surface, thus providing a cylinder of uniform diameter,without the necessity for any re-grinding and without removing thecylinders, etc., from their normal places of use, although of coursethis might be done.

This invention contemplates the use of adherent coatings of one or morematerials which are, applied to the surface as a fluid and which dry orset to provide a hard and even surface. In addition to lacquers andmaterials of that class, resins, metals and plastics may also be used.

Other modifications may be made in the materials used, and in the orderof the steps of the process, and even omitting certain steps, withoutdeparting from the spirit and scope of my invention, and suchmodifications or changes are intended to be covered by the appendedclaims.

I claim:

1. The method of conditioning the surface of a cylinder which consistsin cleaning the surface to be treated, spray coating the surface with alacquer primer, spray coating a metal pigmented lacquer thereover,masking the high spots of the surface with a material to preventformation of a continuous film thereover, spray coating a metalpigmented lacquer over the masked and unmasked portions of the surface,washing off the masked portions, remasking the high spots of the surfaceand recoating the whole surface with metal pigmented lacquer until thelow spots of the surface are built up to the level of the highest areasof the surface, and spray coating the entire surface with a protectivelacquer film.

2'. The method of conditioning the surface of a cylinder which comprisescleaning the surface to be treated, spray coating the surface with alacquer primer, masking the high spots of the surface with a material toprevent formation of a continuous film thereover, spray coating apigmented lacquer over the masked and unmasked portions of the surface,washing off the masked portions, remasking the high spots of the surfaceand recoating the entire surface with pigmented lacquer until the lowspots of the surface are built up to the level of the highest areas ofthe surface, and spray coating the entire surface with a protectivelacquer flhn.

3. The method of conditioning the surface of a cylinder which comprisescleaning the surface of the cylinder to be treated, spray coating thesurface with a base material while rotating the cylinder and drying thecoating while rotating the cylinder to provide an even surface, maskingthe high spots of the surface with a removable material applied from atrue surface, spray coating the masked and unmasked portions of thesurface with a material while rotating the cylinder, removing themasking material and coating thereover, alternately masking the highspots of the surface, coating the surface and removing the maskingmaterial uriiil the low spots are built up to the level of the -ghestareas of the surface, and spray coating the entire surface with aprotective material.

4. The method of conditioning the'surface of a cylinder and the likewhich comprises cleaning and roughening the surface to be treated, spraycoating the surface with a' base priming material, spray coatingthereover a covering material which provides an even surface, maskingthe high spots of the surface with a removable material, and spraycoating the low spots of the surface with at least one layer of build-upmaterial until the same are built up to the level of the highest areasof the surface, and spray coating over the entire surface a protectivematerial.

5. The method of conditioning the surface of a cylinder which comprisespreparing the surface to be treated, applying thereover at least oneadherent, setting coating of material, alternately masking the highspots of the surface with a removable material applied from a truesurface and applying adherent, setting coatings of material to the lowspots of the surface until the same are built up to the level of thehighest areas of the surface, removing the masking material, andapplying at least one adherent, setting coating of materials to providethe desired working face.

6. The method of conditioning the surface of a cylinder which comprisespreparing the surface to be treated, applying thereover at least oneadherent, setting coating of material, alternately masking the highspots of the surface with a removable material applied from a truesurface and applying adherent, setting coatings of material to the lowspots of the surface until the same are built up to the level of thehighest areas of the surface, removing the masking ma terial, andapplying at least one-adherent, setting coating of materials to providethe desired working face, each of said adherent coatings havingdifferent characteristics as to density thereof.

'7. The method of resurfacing and truing the face of a cylinder whichcomprises cleaning and roughening the face of the cylinder, applyingthereover a somewhat resilient base coating, applying thereover acovering coating, alternately masking the high spots of the cylinderface and applying a build-up coating to the low spots of the face untilthe same are built up to the level of the highest areas of the face,removing the masking material, and applying at least one finishingcoating of a nature to produce a hard outer surface.

8. The method of truing the surface of a cylinder which comprisescleaning and preparing the surface to 'be treated, applying thereto anover-all lacquer priming coat, alternately masking the high spots of thecylinder surface and applying abuild-up coating of lacquer to the lowspots thereof until the same are built up to the level of the highestareas of the surface-removing the masking material, and applying atleast one over-all finishing coating of lacquer.

9. The-method of truing the surface of a cylinder which comprisescleaning and roughening the surface to be treated, applying thereto anover-all lacquer'priming coat," applying thereover another lacquercoating, alternately masking the high spots of the cylinder surface andapplying a build-up coating of lacquer to the low spots thereof untilthe same are built up to the level of the highest areas of the surface,re-

spots of the cylinder surface and applying a build-up coating ofpigmented lacquer to the low spots thereof until the same are built upto the level of the highest areas of the surface, removing the maskingmaterial, and applying at least one over-all finishing coating oflacquer.

CHARLES W. LATHAMQ

